The production of gypsum based materials normally requires a slurry of calcium sulfate hemihydrate with water. The mixture is allowed to hydrate, or set to the harder calcium sulfate dihydrate, and the excess water is removed by drying through conventional methods. Gypsum products such as wall board panels are usually produced from a hardened gypsum core sandwiched between liners (e.g., paper liners), with the liners forming the outer surfaces of the board. To overcome problems of water absorption by the hygroscopic gypsum, which may lead to weakening of the wall board, it is known to add hydrophobic components into the gypsum slurry prior to making the wallboards. Such hydrophobic components include wax or silicone emulsions and others.
It has been found that emulsions of a blend of waxes are superior to single waxes in achieving satisfactory water repellency and other qualities. For example, a widely used blend is that of paraffin wax with montan wax.
Montan wax is a hard, fossil-plant wax extracted from certain types of lignite or brown coal. However, there is a major problem with montan wax. It is commercially available in only a few locations, including Amsdorf, Germany (the majority of montan wax coming from there), and in the Ione Basin near Ione in Amador County, Calif. Its rarity casts a shadow of doubt on its continued availability and makes it very expensive.
Attempts have been made to use substitutes for montan wax. For example, U.S. Pat. No. 6,890,976 describes a wax emulsion with a composition made of hydrocarbon wax (e.g., paraffin wax, carnauba wax, polyethylene wax, or maleated hydrocarbon waxes), a polyolefin-maleic anhydride graft polymer, and polyvinyl alcohol (PVA).